A pipeline for enhanced multimodal 2D imaging of concrete structures

We present an imaging pipeline to achieve enhanced images of the interior of concrete from ground penetrating radar (GPR) and ultrasonic echo array (UEA) measurements. This work lays the foundation for an advanced yet practical imaging tool to assess concrete structures. Specifically, we propose an enhanced two-dimensional (2D) total focusing method (XTFM) to reconstruct images from raw GPR and UEA data. The proposed XTFM algorithm integrates total focusing method (TFM) and synthetic aperture focusing technique (SAFT) concepts to post-process large independent and interelement measurements from both modalities in a computationally efficient way. Furthermore, we introduce a novel 2D image fusion algorithm using wavelet multilevel decomposition and an NDT knowledge-based rule to fuse GPR and UEA images. We then compare our algorithm with conventional fusion algorithms such as averaging, maximum, and product. The results from three laboratory concrete reference specimens are evaluated in detail. The fused images are compared with each other as well as benchmarked with the original GPR and UEA images. The output image obtained from our proposed pipeline is an enhanced 2D image of the interior of concrete structures that eases interpretation by a human inspector as well as it has the potential to improve interpretation by computer vision and image analysis algorithms.